Abstract: The variation in operating stages could result in a change of water temperature structure of multiyear regulating storage reservoirs.Thus,understanding of the water temperature dynamics would be essential to study the effect on the downstream water temperature.Using the observational data from the Longyangxia reservoir for the period 1988 to 2008,the variation in reservoir temperature profile and the effect of reservoir operation on the downstream water temperature are studied.The data includes operating stages and reservoir and downstream water temperatures.The result shows the variation in reservoir temperature profile and the effect of reservoir operation on the downstream water temperature is closely related to the reservoir operating scheme.From December to next March,the reservoir water temperature is either weakly stratified or uniformly distributed; higher stages can store more heat,and both reservoir water temperature and downstream water temperature change synchronously with reservoir stages.From May to October,the reservoir water structure is stratified; the stratification is mainly controlled by the reservoir stage,and the downstream water temperature is reversely related to reservoir stages.In the months of November and April,the reservoir temperature structure is rather uniform,and serves as turning points.This study provides valuable information for the determination of the temperature dynamics in large reservoirs and its influence on downstream water temperature.